Molecular tweezers as receptors for anions: An energetic and topological study

The effect of the anion size and dispersion forces on the relative stability of the tweezer-anion complexes are investigated at the DFT and MP2 levels using the series of halide anions. Since the DFT calculations using the B3LYP functional underestimate the dispersion interactions, they show the most electrostatic complexes as the most stables. On the contrary, according to the MP2 calculations the tweezer-Br− complex is the most stable, followed by the tweezer-I− and tweezer-Cl− complexes, these displaying similar interaction energies. On the other hand, DFT calculations on the tweezer-I− complex using the MPW1B95 functional, confirms at the DFT level the important role played by the dispersion interactions on the stability of this complex. The individual anion-π interactions present in the tweezer-anion and the C6F6-anion complexes have been characterized by using the topological analysis of the electron density, finding a straight correlation between structure and topology. As a remarkable result, the correlation between structure and topology in the anion-π systems is shown to be independent on the nature of the anion and on the presence of multiple interactions. This points out to a certain additivity of the anion-π interactions in these systems.